1. Field of the Invention
2. Description of the Related Art
Wind power installations generally have an active drive for wind direction tracking. The active drive rotates the machine housing of the wind power installation in such a way that the rotor blades of the rotor are oriented in the direction of the wind. That drive which is required for wind direction tracking purposes is generally an azimuthal drive which is usually disposed with the associated azimuthal mountings between the tower top and the machine housing. One displacement drive is sufficient when small wind power installations are involved, while larger wind power installations are generally equipped with a plurality of azimuthal drives.
In the procedure involving wind direction tracking of the machine housing, an operating wind-measuring system supplies a mean value for the wind direction over a certain period of time, for example 10 seconds. That mean value is repeatedly compared to the instantaneous azimuthal position of the machine housing. As soon as a deviation exceeds a given value, the machine housing is suitably re-adjusted so that the deviation of the rotor from the wind direction, being the yaw angle, is as small as possible in order to avoid power losses. The way in which wind direction tracking is implemented in the case of known wind power installations is described in “Windkraftanlagen” (“Wind Power Installations”), Erich Hau, second edition, 1995, pages 268 ff and 316 ff respectively.
In previously known wind power installations, motor-powered wind direction tracking of the machine housing, the azimuthal displacement system, takes over the function of automatically orienting the rotor and the machine housing according to the direction of the wind. When considered functionally, the wind direction tracking system is an independent unit. When considered from the point of view of structure, it forms the transition of the machine housing to the tower top. The components thereof are integrated in part in the machine housing and in part in the tower top. The overall system for wind direction tracking comprises the components consisting of the setting drive, holding brakes, locking device, azimuthal mountings and regulating system. Those components operate as follows:
For the setting drive, there are the alternatives hydraulic or electrical, in a similar manner as for the rotor blade displacement drive. Both design configurations are usual in relation to wind power installations. Small installations mostly have unregulated electrical drive motors. In the case of large installations, hydraulic setting drives are in the majority.
A rotary movement-check arrangement or a yaw brake is required in order to prevent the yaw moment about the axis of rotation having to be maintained after the tracking operation has been effected, by drive motors. Otherwise, the service life of the drive assemblies or the upstream-connected transmission assemblies could scarcely be guaranteed. Small installations are generally satisfied with a rotary movement-check arrangement in the azimuthal mounting, while a plurality of releasable holding brakes are known for larger installations. The holding brakes engage a braking ring at the inside of the tower or conversely a ring on the machine housing. During the tracking operation one or two azimuthal brakes are in engagement in order to guarantee the required damping action for the displacement dynamics. In this case the setting drive must be designed in such a way that it can perform the tracking movement against that frictional damping action. The azimuthal or tower top mounting is usually in the form of a rolling bearing assembly.
FIG. 7 is a partly sectional view of a known wind direction tracking system with an electrical setting drive from Westinghaus WT G-0600.
During operation of a wind power installation with turbulent winds—in dependence on the axis of rotation of the rotor—very high forces occur and, linked thereto, high and frequent load peaks in the azimuthal drives.
If there is more than one azimuthal drive, the situation additionally involves a very high degree of asymmetry in the individual drives. Those drives have a step-up transmission ratio by means of a transmission assembly of around 15,000. Very minor deviations in the tooth configuration at the periphery of the tower mounting result immediately in very severe asymmetries if more than one drive, for example four azimuthal drives, are mounted at the periphery of the tower mounting with an integrated tooth arrangement. Because of the high transmission step-up ratio those small deviations on the input side of the drive correspond to up to between 15 and 20 revolutions on the output side.
In consequence this means that, during and after each rotational procedure for the machine housing, the entire load and the entire rotary moment must be uniformly distributed if possible simultaneously to individual drives. In addition, when heavy azimuthal loads are involved, the drives should yield during the stoppage times when excessively high load levels occur, and permit easy rotary movement of the machine housing so that a suitable load relief effect can occur.
In addition, during the wind tracking movement of the machine housing of the wind power installation, in the event of severe turbulence, correspondingly high torques also occur. They excite the azimuthal drives in such a way that the motors oscillate in mutually opposite relationship. In that case the transmission arrangements with their very high step-up transmission ratio react like a spring and the consequence is major torque fluctuations in the individual drives.